DESCRIPTION OF THE PRIOR ART
Hinged type doors that are provided by door manufacturers and distributors generally have a cylinder bore extending from one side to the other side of the door. The cylinder bore is closely adjacent to the edge of the door and typically has a diameter of about 2 1/8inches. The prepared door also has a mortise, which is a hollowed space or rectangular groove, formed at the edge of the door adjacent to the cylinder bore. The mortise typically is 2 1/4 inches high, 1 inch wide, and about 1/8 inch deep. The mortise has a flanged section at the inner end which serves as a stop for a strike plate that covers the mortise after a lock assembly has been installed. Within the mortise, a plunger bore or strike bore is formed extending from the edge of the door to the cylinder bore. The plunger bore has a height of approximately one inch. The plunger bore allows a spring-loaded latching mechanism to project to the door frame or jamb and seat in a groove or recess when the door is closed and to retract into the door in response to the turning of a handle when the door needs to be opened.
When mounting a lock assembly to a door, a cylinder portion of the lock, which may include a tumbler, is inserted and seated in the cylinder bore. The lock assembly includes a mounting plate which has two vertically spaced holes that need to be aligned with through holes that are formed in both sides of the door by the installer prior to installation. During attachment of the lock assembly to the door, longitudinal bolts are passed through the through holes at one side of the door to engage threaded nuts at the other side of the door. After a lock is assembled to the door, the rectangular strike plate is inserted in the mortise flush with the edge of the door.
To aid the installer in preparing the door with the necessary through holes, the packages sold with door lock assemblies include a paper or cardboard template which is used by the installer to drill two through holes in the door. The template has markers printed thereon which indicate where the through holes need to be drilled. During installation, the installer places the template on one side of the door and visually aligns vertical and horizontal centerlines of the template with the visually determined centerlines of the cylinder bore and the plunger bore. With the template held manually in place, the through holes are drilled in one side of the door. The installer then shifts the template to the other side of the door and uses it to drill corresponding holes that must be in alignment with the through holes which were first drilled on the opposing side of the door. The through holes must be spaced vertically at a precise distance of 2.75 inches center-to-center, in accordance with specification standards set by lock manufacturers in cooperation with the construction or building industry. If the through holes are not precisely positioned or if misaligned, the door may be so damaged or defective that it cannot be used. The visual alignment process is apparently time-consuming besides being subject to human error. If the installer needs to install a large number of doors, which occurs with multiple dwellings or office buildings, the problems associated with preparing the through holes are exacerbated.